This issue occurs when the BP editor is open and does not occur with normal camera actors.
I have attached a project to reproduce. The problem occurs when I open BP_CameraActor BP.
1. Create a Blueprint Actor that inherits from the Cine Camera Actor
2. Add Print Node to Tick
3. We can see that Tick is running even if you are not playing
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-101208 in the post.